This application pertains generally to the medical arts and more particularly to an improved self-occluding cannula assembly for insertion into blood vessels or various body cavities.
The invention is particularly applicable to flexible intravascular cannulae of the type commonly used to administer intravenous infusions and/or to monitor pressures within arteries and/or veins of the human body. Accordingly, the invention will be described with particular refererence to such applications. It must be appreciated, however, that the invention has utility in numerous other applications wherein it is desirable to prevent or limit back flow of bodily fluids from a tubular cannula. Examples of other types of cannulae wherein the present invention may be utilized include, but are certainly not limited to; trocars for intra-abdominal or intra-thoracic insertion; long flexible catheters used for monitoring central venous pressures and for centrally administering drugs and various infusates; and various indwelling semi-permanent catheters such as the type commonly used in the administration of total parenteral alimentation.
Although many of the cannulae in which the invention will be used may incorporate removable introducer needles or stylets to effectuate puncture of soft tissues, it must be further appreciated that the utility of the invention is not limited to such needle-bearing devices. In fact, the occluding means of the present invention may be employed with even the simplest types of medical tubing to prevent back flow of fluids therefrom.
It is common practice in the medical field to insert tubular cannulae into blood vessels for the infusion of various fluids and/or the monitoring of intravascular pressures. One simple intravenous cannula assembly of the prior art comprises a flexible cannula sheath having a rigid introducer needle positioned axially therewithin. The bevelled tip of the hollow introducer needle extends a short distance beyond the distal tip of the cannula to permit easy penetration of the skin and underlying tissues. When the needle tip enters the target blood vessel, blood immediately fills the lumen of the needle and advances proximally to a transparent receptical on the needle hub where it may be readily viewed. Alternatively the needle hub may be connected to a syringe wherein a small amount of the blood may be visably withdrawn into an existing quantity of saline solution. Thereafter, the introducer needle is withdrawn. Thus, the cannula sheath remains in place as a means for subsequent infusion of intravenous fluids and/or monitoring of intravascular pressures.
Because the flexible cannula sheath comprises a generally hollow tube, blood will rapidly back flow (i.e. flash back) through the inner lumen of the cannula upon withdrawal of the introducer needle. As a result, a certain amount of blood invariably flows out of the proximal end of the cannula immediately after withdrawal of the introducer needle. Regardless of how adept the user may be at attaching an appropriate solution administration line or other auxiliary tube to the proximal end of the cannula, a certain amount of blood loss is likely to occur.
Likewise, if the attendant solution administration line or other tube subsequently becomes disconnected from the cannula, blood will immediately back flow from the cannula and may continue to flow therefrom until the disconnected line is discovered and reconnected.
Indeed, any unnecessary back flow of blood from the cannula lumen is undesirable from a standpoint of general hygene as well as in view of the present potential for blood born disease transmission. Serious diseases such as Hepatitis and Acquired Immune Difficiency Syndrome are known to be transmissible to health care workers and others who come in contact with infectous blood.
Thus given the desirability of preventing the unnecessary back flow and leakage of blood from the cannula, a number of arrangements have been devised whereby the user of the cannula may pinch off or otherwise obstruct the cannula lumen. Examples of such prior art devices are found in U.S. Pat. Nos. 3,875,935 (Mellor), 2,682,874 (Hickey), 4,192,304 (Millett), 3,856,020 (Kovac), and 3,856,010 (Moorehead). These prior United States Patents disclose various means for valving, blocking, clamping, pinching, or otherwise restricting certain types of medical tubing for purposes of preventing fluid back flow thererfrom.
Specifically, U.S. Pat. No. 4,192,304 (Millett) describes an intravascular catheter assembly comprising a pliable cannula sheath, having an introducer needle disposed axially therewithin. A pair of laterally extending external wings are formed on the the proximal end of the cannula. One of the wings bears a pinching protuberance. Upon withdrawal of the introducer needle, the user of the cannula may manually fold one of the wings over the cannula body so as to cause the pinching protuberance to exert occluding pressure on the cannula. Thus, so long as pressure is applied to the folded wing, the pinching protuberance will effectively occlude the cannula lumen. Such occlusion is purported to prevent undesirable back flow of fluids from the cannula.
Another exemplary prior art device is described in U.S. Pat. No. 3,856,010 (Moorehead). The device described therein comprises a flexible cannula sheath having an introducer needle disposed axially therewithin. The Moorehead further incorporates a resilient means which is manually compressable to control the flow of fluid through the cannula. As the introducer needle is withdrawn, the user must positively and affirmatively apply pressure to a projection, which upon passage of the needle, results in closure of a valve member so as to prevent the flow of fluid through the cannula lumen. Upon release of such pressure, the valve member relaxes, and the cannula lumin resumes its normal shape permitting free fluid flow therethrough.
Yet another exemplary prior art device is disclosed in U.S. Pat. No. 3,875,938 (Mellor). The Mellor device includes a bifurcated cannula assembly wherein a needle-like "puncture rod" is disposed axially within a flexible cannula sheath. The Mellor device includes a means whereby the user may pinch off the cannula lumen between the time that the "puncture rod" is removed and the subsequent coupling of auxilliary infusion tubing to the proximal end of the cannula.
At least one other intravenous cannulation device of the prior art employs a bifurcated design wherein a separate side arm or secondary infusion port is provided in addition to a proximal extension of the lumen through which the introducer needle is withdrawn. The introducer needle may thus be withdrawn through a latex membrane, flap-like seal, or other sealing closure located separate and apart from the side arm infusion port. Thereafter, the infusion of fluid, withdrawal of blood or monitoring of pressures is carried out through the side arm port while the sealed channel through which the needle was withdrawn remains usable only as a self sealing injection port for the periodic injection of medications, or piggyback administration of a second intravenous fluid.
While each of the prior art devices may indeed be capable of stopping or at least limiting, the back flow of blood from certain types of tubes in certain situations, it must be appreciated that none of the prior art devices provides an occlusion means that is fully self activating (i.e. user passive) so as to automatically halt the flow of fluid through the cannula upon withdrawal of the introducer needle and subsequently capable of re-occluding the cannula upon inadvertent disconnection of any attendant infusion/monitoring line. Indeed, many of the prior art occlusion devices require rather intricate manual manipulation and constant manual attendance in order to effect occlusion of the cannula lumen. Additionally, prior art devices which incorporate elaborate secondary infusion ports, side arms, and other bifurcated arrangements may be expensive to manufacture and confounded with unnecessary complexity in clinical use.
Accordingly, there currently exists a need in the art for a fully self-actuating occlusion means which will serve to passively, automatically occlude the cannula lumen upon withdrawal of an existing introducer needle as well as to subsequently re-occlude the cannula lumen upon inadvertent disconnection of any infusion and/or monitoring line from the proximal end of the cannula. The present invention overcomes these shortcomings of the prior art in addition to providing other advantages over the existing devices.